Sulfonated polybenzimidazole/zirconium phosphate composite membranes for high temperature applications

Sulfonated polybenzimidazoles (SPBI) with different sulfonation degrees were prepared from 3,3′,4,4′-amino-diphenyl ether, 5-sulfonated isophthalate sodium and isophthalic acid by direct polycondensation in polyphosphoric acid. Considering the conductivity and oxidative stability of the SPBIs with different sulfonation degrees, the SPBI-10 membrane was optimally selected as base membrane. In order to enhance the proton conductivity, Zirconium phosphate (ZrP) was physically mixed with SPBI-10 to get a serial of composite membranes. The water uptake rises slightly with the increase of ZrP and the phosphoric acid swelling ratio of membranes greatly depends on the concentration of phosphoric acid, dipping time and temperature. At the H3PO4 doping level of 5, the phosphoric acid swelling ratio is up to 15%, and the membranes keep a good mechanical property. Due to the addition of ZrP, the conductivity of SPBI-10-Z3 composite membrane is up to 0.08S/cm at 180 °C, which increases about 20% compared with that of SPBI-10 membrane. This suggests that SPBI/ZrP composite membranes may be a promising polymer electrolyte for high temperature PEMFCs.